html: don't emit text token for empty raw text elements.
Andrew Balholm authored
Pass tests1.dat, test 99:
<script></script></div><title></title><p><p>

| <html>
|   <head>
|     <script>
|     <title>
|   <body>
|     <p>
|     <p>

Also pass tests through test 105:
<ul><li><ul></li><li>a</li></ul></li></ul>

R=nigeltao
CC=golang-dev
https://golang.org/cl/5373043
ddc5ec64